[libpng17] Enable parallel tests and rearrange TESTS order to take advantage of

the massive speed improvements use a make capable of parallel builds
on a multi-CPU machine and pass the right arguments to make (-j10000
for GNU make) to get the build to run in parallel.

tests/pngunknown-sAPI

@@ -0,0 +1,2 @@
+#!/bin/sh
+exec ./pngunknown bKGD=save cHRM=save gAMA=save all=discard iCCP=save sBIT=save sRGB=save "${srcdir}/pngtest.png"